In the related art, an image forming apparatus using developer of two-component mixture containing a carrier and a toner is known. The carrier is a substance which is stirred with toner particles in a container and which imparts electric charge to the toner particles and conveys the toner to a surface of a photoconductive substance.
In the image forming apparatus, when an image is formed on a sheet in a state where a printing rate is low, a toner inside a developing container may be degraded. In particular, toner for low temperature fixation which is recently provided in a market may be fixed on a sheet at a low temperature while the toner has low thermal resistance characteristics and is easily soluble and thus, an external additive on a surface of toner may be easily embedded into or separated from the toner surface. Especially, when stirring is continued in a state where the developer is not replaced, an external additive is embedded into or separated from the surface of toner as described above and developing capability to an image carrier (photoconductive drum) is lowered.
For that reason, a degraded toner needs to be replaced with a supplying toner regularly (refresh operation). In this context, an image forming apparatus that performs a determination whether a replacement of a toner is needed or not based on a time at which developing is performed or the number of sheets subjected to print processing, and a printing rate per a single sheet, and replaces the toner is known.
However, in the related art, a cumulative counter is reset after the toner replacement operation is performed, without determining whether the degraded toner is sufficiently output. Accordingly, whether effective developing may be performed is uncertain. Although the toner replacement operation is performed, when the degraded toner is not sufficiently output, effective developing may not be performed.